1. Field of the Invention
The present invention relates to the flux method for producing a Group III nitride compound semiconductor crystal, in which a Group III nitride compound semiconductor crystal is grown by use of a flux.
The method of the present invention is effective for reducing semiconductor crystal dislocations or crack density, as well as semiconductor crystal production cost.
2. Background Art
Techniques which have hitherto been known for growing a Group III nitride compound semiconductor crystal through the flux method include those disclosed in, for example, Japanese Patent Application Laid-Open (kokai) Nos. H11-060394, 2001-058900, 2001-064097, 2004-292286, and 2004-300024.
Such a conventional production method generally employs, as a base substrate (seed crystal), a template formed by providing a semiconductor layer (e.g., a buffer layer) on a sapphire substrate, a GaN single-crystal free-standing substrate, or a similar substrate.
In the method disclosed in any of the aforementioned patent documents, a seed crystal is immersed in a flux containing a dissolved Group III element, while an N-containing gas is supplied to the flux, followed by pulling of the seed crystal from the flux.
In the case where a template substrate formed by growing GaN on a sapphire substrate through MOCVD is employed as a seed crystal, when a target Group III nitride compound semiconductor crystal is grown on the seed crystal to a large thickness, a large number of cracks are generated in the semiconductor crystal during removal of the semiconductor crystal from a reaction chamber, because of a great difference in thermal expansion coefficient between the semiconductor crystal and the sapphire substrate. Therefore, when the aforementioned template is employed as a base substrate, difficulty is encountered in producing, for example, a semiconductor crystal of high quality having a thickness of 400 μm or more.
If a GaN single-crystal free-standing substrate is employed as a base substrate, generation of cracks in a target semiconductor crystal may be suppressed, since there is no difference in thermal expansion coefficient between the semiconductor crystal and the base substrate. However, difficulty is encountered in reducing production cost, since a GaN single-crystal free-standing substrate is expensive.
Meanwhile, no supply of a Group III element to a flux during growth of a semiconductor crystal raises a problem in that the Group III element content of the flux is reduced in accordance with progression of growth of the semiconductor crystal, resulting in a decrease in crystal growth rate.